Effect of nozzle geometry and attached porous layer on jet impingement heat transfer of a flat plate
羅翊文、吳佩學
E-mail: [email protected]
ABSTRACT
Jet impingement is an important heat transfer technique in industries, such as metal and glass annealing, laser cooling, gas turbine blade cooling, and cooling of microelectronics. Nowadays, enhancement techniques for jet impingement heat transfer are still under intensive investigation by academic researchers. In this study, the enhancement of impingement heat transfer on a flat plate covered with a thick layer of porous medium with or without a center hole was numerically investigated. The renormalization group (RNG) turbulence model is selected for the fluid region while Forchheimer extended Darcy’s model is used for porous region. The numerical modeling was justified by comparisons with available experimental data. A modification to the existing model which shows drawbacks for high Reynolds number applications is also suggested in this study. Computational results show that an attached porous medium having a sufficiently deep center hole can effectively enhance jet impingement heat transfer while an attached thick porous layer without a center hole, or having a center hole with insufficient depth, has detrimental effect. The physics of these results are supported and well explained by the detailed flow patterns. Under the condition of fixed porosity and permeability, the
influential parameters for the investigated heat transfer problem include the jet Reynolds number, nozzle geometry (including nozzle length and jet-to-hole diameter ratio), jet-to-plate distance, and the center hole depth. A good hole geometry should well trap the jet and direct the coolant along the heated plate. The heat transfer performance is the best when the jet-to-hole diameter ratio equals one. To give better heat transfer performance, the nozzle should be shorter, resulting in more uniform flow at the exit, at low Reynolds numbers, and it should be long enough at high Reynolds numbers so that the exit flow is fully developed. Finally,
corre3lations of Nusselt number versus Reynolds number are proposed for the investigated problem. It is hoped that the correlations are helpful to the designers who will use an attached porous layer in an impingement cooling design.
Keywords : jet impingement、porous medium、center hole、numerical modeling、center hole depth、Reynolds number Table of Contents
封面內頁 簽名頁 博碩士論文暨電子檔案上網授權書...iii 中文摘要...iv ABSTRACT...vi 誌 謝...viii 圖目錄...xi 表目錄...xiii 符號說明...xiv 第一章緒
論...1 1.1研究背景...1 1.2研究目的...2 第二章 文獻回顧...5 第三章問題描述與數值模 型...12 3.1各模擬幾何形狀與網格...12 3.2基本假設...12 3.3統御方程式...13 3.4離散方
法...20 3.5數值計算...21 3.5.1. 收斂條件...21 3.5.2. 鬆弛因子...22 第四章平板加入多孔材之 模擬與討論...26 4.1完全發展流與均勻流的差異...26 4.2中心孔深度的影響...26 4.3雷諾數的影響...27 4.4噴 嘴幾何的影響...28 4.4.1 噴嘴直徑的影響...28 4.4.2 噴嘴長短的影響...29 4.5噴嘴與平板間距離的影
響...30 4.6雷諾數與紐賽數之關係...31 4.7總結...32 第五章結論...54 參考文 獻...56
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